I'm not seeing the classic signs of severe underextrusion. Are you refererring to the fact that the wall is not well bonded to the infill and top layer? I would guess that's probably due to the outer shell cooling down before it gets around to adding the infill. It could also be due to your very thin wall curling away from the body.
I can think of a number of tweaks that might help. "Infill overlap" as suggested by Dodgrr might certainly do the trick. Or, raising the filament temperature a bit, increasing the shell thickness way more than what you have (I like 1.2mm when I want a high quality print), reduce layer thickness to 0.1. Some might suggest playing with the fan, but I'd be wary of that.
Also I find gray tends to be the most likely to underextrude of the colors I have tried from UM. Plus .25 is a pretty large layer height, so I would try decreasing the layer height for your next print. Specially with gray.
very weird.. kinda looks like a "material availability" issue, maybe crank up your print head temp a few degrees, could try tighting the feeder tension a bit too after making sure no plastic bits are cought in the teeth of the knurled wheel. impressive note-taking btw!
Well done. One tip: the clip on part on Robert's feeder is really only needed as support for flexible filament. For PLA etc I prefer to remove that so I can see the filament better, blow that area clean etc.